In an ion beam irradiating apparatus which irradiates a target with an ion beam extracted from an ion source, thereby performing ion implantation or another process, it is desired to efficiently transport a low-energy and large-current ion beam from viewpoints such as that the throughput of the apparatus is improved, and that the ion implantation depth is reduced to cope with miniaturization of a semiconductor device to be formed on the target.
As the energy of an ion beam is lower and the current of the beam is larger, however, dispersion of the ion beam due to space charge is further increased, and hence it is difficult to efficiently transport the ion beam. As one technique for solving the problem, a technique is known in which electrons are supplied from the outside to a transported ion beam and space charge of the ion beam is neutralized by the electrons.
In this case, it is preferable to use an electron source which can generate a large amount of low-energy electrons because of reasons such as that negative charging of the surface of a target by the supplied electrons is suppressed.
As an electron source which can generate a large amount of low-energy electrons, Japanese Patent Unexamined Publication No. 2005-26189 (Paragraphs 0007 to 0009, FIG. 1) (hereinafter referred as Patent Reference 1) discloses a field emission electron source. Namely, the publication discloses a technique in which a field emission electron source that can generate a large amount of low-energy electrons is placed in the vicinity of a target, electrons emitted from the field emission electron source are caused to be incident substantially perpendicularly on an ion beam from the lateral side of the ion beam, and charging (charge-up) of the surface of the target at ion-beam irradiation is suppressed.